Stud-weldable rebar

ABSTRACT

A stud-weldable rebar and a method for making the rebar are disclosed. The rebar has a steel body with a weld end and a diameter that is substantially uniform along a length of the body. A tip portion at the weld end includes a hardened zone and a base portion is formed of the remaining steel body. The hardened zone has a hardness that is about 1.5-3.0 times greater than a hardness of the base portion. Induction hardening is used to form the hardened zone.

BACKGROUND

The present disclosure relates to deformed reinforcing bar (“rebar”)products along with methods for forming the same. Although the rebar isparticularly useful for stud-welding to other base metals, the rebar isprimarily used in concrete reinforcement applications where specificindustry standards must be met, such as reinforced concrete structureswhich are subject to seismic activity.

Rebar and deformed bar products are manufactured to meet specificindustry standards, such as ASTM International DesignationA706/A706M-16, Standard Specification for Deformed and Plain Low-AlloySteel Bars for Concrete Reinforcement (“ASTM A706/A706M”), the contentsof which are incorporated herein. Rebar and deformed bar products usedin structures subject to seismic activity must also meet therequirements set forth in American Concrete Institute 318-14, BuildingCode Requirements for Structural Concrete (“ACI 318-14”), the contentsof which are also incorporated herein. ASTM A706/A706M compliant steelis commonly used for the reinforcement of concrete in seismic-riskareas.

Certain structures require the fastening of rebar to a base metal. Onetechnique for fastening rebar to a base metal includes the use ofthreaded ends and fasteners. However, this technique can be timeconsuming and requires additional equipment to manufacture and assemblethe rebar and base metal structure. Another technique for fasteningrebar to a base metal includes welding. The “weldability” of barproducts is generally dependent on chemical composition and the carbonequivalent value (“CEV”) of the material used to manufacture the barproduct. The standards in ASTM A706/A706M incorporate limited chemicalcompositions and CEVs for weldable material and recommend compliancewith the American Welding Society D1.1/1.1M:2015, Structural WeldingCode for Steel (“AWS D1.1/1.1M”), the contents of which are additionallyincorporated herein. However, while some materials and welding processesare compliant with the aforementioned standards, they neverthelesssuffer drawbacks such as being time consuming and requiring specializedpre-treatments and equipment.

Stud-welding is a fastening process that improves rebar and base metalassembly time. However, the steel material used to form the rebar mustbe selected to have a lower CEV range than the maximum allowed in ASTMA706/A706M, otherwise the steel rebar would not be “stud-weldable”.Moreover, existing stud-weldable rebar made from ASTM A706/A706Mcompliant steel still requires additional physical deformation steps andspecialized equipment, which ensue increase in cost and difficulty ofmanufacturing.

It would be desirable to develop a new stud-weldable rebar formed fromASTM A706/A706M compliant steel which overcomes the drawbacks of theprior art, such as those discussed above.

BRIEF DESCRIPTION

The present disclosure relates to rebar products suitable for concretereinforcement in applications where mechanical properties are controlledto achieve necessary tensile and yield strength. The present disclosurealso relates to steel rebar made from a material with a restrictedchemical composition necessary to achieve stud-weldability.

In accordance with one aspect of the present disclosure, a stud-weldablerebar is provided that has a steel body with a weld end and a diameterthat is substantially uniform along a length of the body. The body has atip portion at the weld end and a base portion formed of the remainingsteel body. The tip portion includes a hardened zone with a hardnessthat is about 1.5-3.0 times greater than a hardness of the base. Moreparticularly, the hardness of the hardened zone is about 2-2.5 timesgreater than the hardness of the base portion. As measured on theRockwell scale, the hardness of the hardened zone is about 20-50 HRC.The hardened zone has a length, and the length of the hardened zone isabout 30-50% the diameter of the body. More particularly, the length ofthe hardened zone is about 40% the diameter of the body. The tip portioncan further include a terminal surface at the weld end and a chamferededge that is located adjacent the terminal surface. The chamfered edgeextends a length that is about 20-45% the length of the hardened zone.More particularly, the chamfered edge length extends about 22.5-40% thelength of the hardened zone. The tip portion further includes a fluxload fixed to the terminal surface at the weld end and The flux load hasa length that is about 10-25% the length of the hardened zone. Moreparticularly, the length of the flux load is about 12.5-20% the lengthof the hardened zone. The chemical composition of the steel bodyincludes 0.08-0.23 wt % of carbon, 0.95-1.2 wt % of manganese, less than0.25 wt % of copper, less than 0.15 wt % of nickel, less than 0.15 wt %of chromium, 0.001-0.05 wt % of molybdenum, and 0.03-0.08 wt % vanadium.More particularly, the chemical composition of the steel body includes0.08-0.23 wt % of carbon, 0.95-1.2 wt % of manganese, less than 0.04 wt% of phosphorous, less than 0.05 wt % of sulfur, 0.2-0.4 wt % ofsilicon, less than 0.25 wt % of copper, less than 0.15 wt % of nickel,less than 0.15 wt % of chromium, 0.001-0.05 wt % of molybdenum,0.001-0.02 wt % of aluminum, 0.03-0.08 wt % vanadium, less than 0.0005wt % of boron, and less than 0.02 wt % of nitrogen. In any event, thechemical composition of the steel body includes a carbon equivalencyvalue between 0.31-0.42%.

In accordance with another aspect, a method of forming a stud-weldablerebar is disclosed. The method includes providing a steel body with aweld end and a diameter that is substantially uniform along a length ofthe body. Next, the method includes heating a portion of the weld endfor about 4-9 seconds until the portion of the weld end reaches a targettemperature of about 1,300-1,700° F. Then, the heated portion of theweld end is allowed to rest for a dwell time of about 2 seconds.Finally, the method includes cooling the heated portion of the weld endby quenching in a cooling medium for about 5-12 seconds. As a result,the hardness of the weld end portion is increased by about 1.5-3 timesthe hardness of the remaining portion of the steel body. Moreparticularly, the hardness of the hardened weld end portion is about20-50 HRC. The length of the hardened weld end portion is about 40% thenominal diameter of the steel body. The method also includes providing asteel body having a chemical composition of 0.08-0.23 wt % of carbon,0.95-1.2 wt % of manganese, less than 0.04 wt % of phosphorous, lessthan 0.05 wt % of sulfur, 0.2-0.4 wt % of silicon, less than 0.25 wt %of copper, less than 0.15 wt % of nickel, less than 0.15 wt % ofchromium, 0.001-0.05 wt % of molybdenum, 0.001-0.02 wt % of aluminum,0.03-0.08 wt % vanadium, less than 0.0005 wt % of boron, and less than0.02 wt % of nitrogen. The method further includes restricting thechemical composition of the steel body to a carbon equivalency valuebetween 0.31-0.42%.

In accordance with yet another aspect, a stud-weldable rebar isdisclosed which includes a steel body having first end, a weld end, anda cylindrical outer surface. The cylindrical outer surface defines adiameter that is substantially uniform along all points of the steelbody. A tip portion at the weld end includes a hardened zone, a terminalsurface, and a flux load fixed to the terminal surface. A base portionis defined between the first end and the tip portion of the steel body.The hardened zone has a length that is about 30-50% the total diameterof the steel body and a hardness that is about 1.5-3.0 times greaterthan the hardness of the base portion of the steel body. Moreparticularly, the hardness of the hardened zone is about 20-50 HRC andthe hardness of the base portion of the steel body is about 90-98 HRB.In addition, the length of the hardened zone is more particularly about0.150-0.400 inches.

These and other non-limiting characteristics of the disclosure are moreparticularly disclosed below.

BRIEF DESCRIPTION OF THE DRAWINGS

The following is a brief description of the drawings, which arepresented for the purposes of illustrating the exemplary embodimentsdisclosed herein and not for the purposes of limiting the same.

FIG. 1 is a side view of a deformed reinforcing bar according to thepresent disclosure which includes a hardened zone formed on a weld endof the bar;

FIG. 2 is a side view of the tip portion of the deformed reinforcing barof FIG. 1 which has been enlarged to more clearly show the elements andfeatures of the tip portion;

FIG. 3 is a transverse right-angled cross-section of the deformedreinforcing bar in FIG. 1 taken on the plane of line AA; and,

FIG. 4 is a transverse right-angled cross-section of the deformedreinforcing bar in FIG. 1 taken on the plane of line BB.

DETAILED DESCRIPTION

A more complete understanding of the components, processes andapparatuses disclosed herein can be obtained by reference to theaccompanying drawings. These figures are merely schematicrepresentations based on convenience and the ease of demonstrating thepresent disclosure, and are, therefore, not intended to indicaterelative size and dimensions of the devices or components thereof and/orto define or limit the scope of the exemplary embodiments.

Although specific terms are used in the following description for thesake of clarity, these terms are intended to refer only to theparticular structure of the embodiments selected for illustration in thedrawings and are not intended to define or limit the scope of thedisclosure. In the drawings and the following description below, it isto be understood that like numeric designations refer to components oflike function.

The term “about” can be used to include any numerical value that canvary without changing the basic function of that value. When used with arange, “about” also discloses the range defined by the absolute valuesof the two endpoints, e.g. “about 2 to about 4” also discloses the range“from 2 to 4.” The term “about” may refer to plus or minus 10% of theindicated number.

The rebar described in the present application is produced from a lowcarbon steel having a restricted chemical composition that complies withindustry standards set forth in ASTM A706/A706M. The dimensional andstrength requirements detailed in ASTM A706/A706M are also met by therebar product described in the present application.

As used herein, the terms “steel”, “A706 steel”, “low-alloy steel”, “lowcarbon steel”, etc., can be used interchangeably and generally refer toa steel material that meets the requirements set forth in ASTMA706/A706M. Moreover, when used herein, these material-related termsgenerally refer to bars made of “Grade 60” steel, defined in ASTMA706/A706M as having a minimum yield strength of 60,000 psi. However,the concepts in this application can apply equally to other steelswithout departing from the scope of the disclosure. For example, “Grade80” steel, defined in ASTM A706/A706M as having a minimum yield strengthof 80,000 psi, could also be used. Similarly, while deformed reinforcingbars are specifically referred to herein, the concepts of thisapplication can apply equally to plain reinforcing bars withoutdeparting from the scope the disclosure.

The steel material used to form the rebar of the present disclosure hasa composition that also meets the stud-weldability requirements setforth in AWS D1.1/1.1M-15. The “stud-weldability” of the presentlydisclosed rebar is achieved by induction hardening of a tip portion ofthe rebar to form a hardened zone at the weld end of the bar. In thisregard, the hardened zone essentially divides the rebar into a tipportion containing the hardened zone and a softer base portion. Aspecific length and Rockwell hardness define the induction hardened zoneas discussed in further detail below. The “stud-weldability” of therebar described herein provides a more practical and time saving methodfor attaching rebar to a base metal. The rebar and base metal assemblyprocess is commonly required in concrete reinforcement applications,including the construction of structures which are prone to seismicactivity. As such, the presently disclosed rebar is further compliantwith the standards set forth in ACI 318-14.

FIG. 1 is a side view of a section of rebar 100 in accordance with thepresent disclosure. FIG. 2 is a side view of a tip portion of the rebar100 which has been enlarged to more clearly show the elements andfeatures thereof. FIGS. 3 and 4 illustrate transverse right-angledsections of the rebar 100 taken along planes of the lines A-A and B-B,respectively. Stock rebar material (not shown) is generally provided incoil or long stock form. Desired length sections of rebar can be cutdirectly from long stock, whereas coil stock usually needs to bede-coiled before cutting.

Rebar 100 can be cut from coil or long stock to form a longitudinal bodysection 102 that extends a length L_(R) along axis X. The rebar body 102includes a first end 104 and a second or weld end 106. An outer surface108 is generally cylindrical in shape and defines a diameter D of thebody 102. As illustrated in FIGS. 1, 3, and 4, a plurality ofribs/deformations 110/112 can be formed on the outer surface 108. Theribs/deformations 110/112 project outward from the outer surface 108 toa height H, as is typical in deformed reinforcing bars. Ignoring theheight H of any ribs/deformations that may be present and/or any otheroptional surface features of the rebar body 102 (e.g., chamfered edgeportion 116 described in further detail below), the rebar diameter D issubstantially uniform at all points along length La.

Each rib/deformation 110/112 can be formed to have the same or differentheight as other ribs/deformations in the plurality. The presentapplication is not limited by specific values for the height H of theribs/deformations 110/112. However, ASTM A706/A706M provides values forthe minimum average height of deformations depending on the nominal barsize or diameter, along with other general requirements and guidelinesfor deformation height. Rebar made according to the present disclosurewould generally follow these requirements and guidelines. Moreover,several shaped regions are defined between adjacent ribs/deformations onthe outer surface 108 of the rebar body 102. These shaped regions helpanchor the rebar to an associated construction material such asconcrete. While the ribs/deformations 110/112 are illustrated as havinga specific size, shape, arrangement, etc., these characteristics arenon-limiting and can be changed as desired to suit a variety ofdifferent circumstances and applications, provided the requirements setforth in ASTM A706/A706M and the additional limitations set forth beloware met.

As best shown in FIGS. 1 and 2, a tip portion 122 of the rebar body islocated at the second or weld end 106. The tip portion 122 generallyincludes terminal surface 114, one or more optional surface featuressuch as chamfered edge 116, flux load 118, and hardened zone 120. Theremaining portion of rebar body, i.e., the portion of body other thantip 122, is referred to as a base portion 124. In other words, baseportion 124 generally refers to the portion of rebar body 102 that isbetween the first end 104 and the tip portion 122. The terminal surface114 of the tip portion 122 is generally flat and extends transversely toaxis X. However, the specific shape of the terminal surface isnon-limiting. For example, the terminal surface could be hemisphericalin shape instead of flat.

The optional chamfered edge 116 of tip 122 can be included to transitionbetween the outer surface 108 of the rebar body 102 and terminal surface114. As illustrated, the chamfered edge 116 slopes radially inward at adesired angle α and for a desired length L_(E) along axis X. The lengthL_(E) which chamfered edge 116 extends can be increased or decreaseddepending on the diameter D of the rebar body 102, however this is notrequired. As discussed in further detail below, the length L_(E) whichchamfered edge 116 extends can also be related to the size of thehardened zone 120. In some particular embodiments, the chamfered edge116 slopes radially inward at an angle α of about 43 degrees to about 47degrees, including about 45 degrees. However, at other angles can alsobe used without departing from the scope of the present disclosure.Various exemplary chamfered edge lengths L_(E) are provided in Table 1below.

The flux load 118 is disposed on the terminal surface 114 of the tipportion 122 at weld end 106. The flux load 118 is a ball of aluminumthat is subsequently embedded, pressed, or otherwise fixed to theterminal surface 114. In this regard, the terminal surface 114 caninclude a pre-formed depression (not shown) where the metal ball isembedded, pressed, or otherwise affixed to form the flux load 118. Afterbeing fixed to the terminal surface, the flux load 118 extends out ofthe terminal surface a length L_(F) along axis X. The size (i.e., lengthL_(F)) of the flux load 118 can be increased or decreased depending onthe diameter D of the rebar body 102, however this is not required. Asdiscussed in further detail below, length L_(F) of the flux load 118 canalso be related to the size of the hardened zone 120. Various exemplaryflux load lengths L_(F) are provided in Table 1 below.

The tip portion 122 at the weld end 106 also includes a zone where atleast one mechanical property has been modified. More particularly, thetip includes a hardened zone 120 at the weld end 106 that is formed byrapid heating and cooling. The heating is preferably achieved byinduction heating, followed by a rapid quench in a cooling medium suchas water. The induction hardening process used herein advantageouslyproduces a martensitic microstructure at hardened zone 120 which isharder than the base A706 material used to form rebar 100. In addition,the martensitic microstructure extends from the outer surface to thecore of the rebar body 102 at hardened zone 120. Induction heating isalso advantageous because it permits hardening of a selected area (e.g.,hardened zone 120) without significantly affecting the mechanicalproperties of the portions of rebar surrounding the selected area. As aresult, the tip portion 122 (excluding flux load 118) has a greaterhardness than the base portion 124 of the rebar body 102. It should benoted that the flux load 118 of the tip portion 122 can be fixed to theterminal surface 114 before or after zone 120 has undergone hardening.However, regardless of whether the flux load is fixed before or afterinduction hardening, the hardness properties of flux load areindependent from those of the hardened zone.

As shown in FIGS. 1 and 2, the hardened zone 120 extends longitudinallyalong axis X for a length L_(Z). The size (i.e., length L_(Z)) of thehardened zone 120 can be increased or decreased depending on thediameter D of the rebar body 102, however this is not required. In manyapplications, the relationship between hardened zone length L_(Z) andrebar diameter is that larger rebar sizes will require larger hardenedzones at the weld end. In other words, the length L_(Z) of the hardenedzone is directly proportional to the diameter of the rebar. Variousexemplary lengths L_(Z) for the hardened zone 120 are provided in Table1 below.

In some embodiments, the hardened zone 120 has a length L_(Z) that isabout 30-50% the rebar diameter D. Preferably, the length L_(Z) of thehardened zone 120 is about 40% the rebar diameter D. Rebar is commonlyprovided in nominal diameters of ⅜″, ½″, ⅝″, ¾″, ⅞″, and 1″. Thus, whenthe diameter D of rebar body 102 is equal to these nominal sizes, thepreferred length L_(Z) of hardened zone 120 is from about 0.150″ toabout 0.400″. Based on these hardened zone sizes, the chamfered edge 116can extend a length L_(E) that is about 20-45% the length L_(Z) of thehardened zone 120. Preferably, the chamfered edge 116 extends a lengthL_(E) that is about 22.5-40% the length L_(Z) of the hardened zone 120.In addition, the flux load 118 can have a length L_(F) that is about10-25% the length L_(Z) of the hardened zone 120. Preferably, the fluxload 118 has a length L_(F) that is about 12.5-20% the length L_(Z) ofthe hardened zone 120.

In some embodiments, the hardened zone 120 of the tip portion 122 has ahardness that is about 1.5-3 times greater than a hardness of the baseportion 124. Preferably, the hardened zone 120 is about 2-2.5 timesharder than the base portion 128 of the rebar body 102. In other words,the hardening process described herein increases the hardness of zone120 at the weld end 106 by about 120-150% compared to the rest of rebarbody 102. In some particular embodiments, the hardened zone 120 has aRockwell hardness of about 20-50 HRC, and the base portion 124 has aRockwell hardness of about 90-98 HRB. Importantly, it should be notedthat the induction hardening process penetrates to the core of the rebarbody 102, such that the hardness of about 20-50 HRC is present from theouter surface to the core at the hardened zone 120.

Table 1 below provides exemplary values for the dimensional variablesillustrated in FIGS. 1-4 and discussed above, including diameter D,length L_(R) of the rebar body, size or length L_(F) of the flux load,size or length L_(Z) of the hardened zone, and length L_(E) of thechamfered edge. The rebar diameters listed in Table 1 correspond tonominal bar sizes that are commonly available in the industry. Table 1also provides preferred values for “burn-off”, which refers to theamount of rebar body 102 consumed during stud welding at the weld end106. The “burn-off” material generally forms the weld fillet.

TABLE 1 Preferred Values for the Dimensional Variables of theStud-Weldable Rebar Rebar Rebar length Flux Hardened zone Chamfered edgeBurn- diameter (L_(R)), in., length length (L_(Z)), length (L_(E)), in.,Off, (D), in. ±0.031 (L_(F)), in. in., +.062/−.000 α = 45°, ±2 in. ⅜8-120 0.030 0.150 0.060 0.1250 ½ 8-120 0.030 0.200 0.070 0.1250 ⅝ 8-1200.040 0.250 0.090 0.1875 ¾ 8-120 0.050 0.300 0.090 0.1875

The materials from which rebar and deformed bar products aremanufactured are required to meet specific industry standards. Thematerial used to form the stud-weldable rebar 100 of the presentdisclosure meets the requirements set forth in ASTM A706/A706M. In otherwords, the stud-weldable rebar 100 is manufactured from A706 steel,grade 60, as set forth in ASTM A706/A706M. In addition, thestud-weldable rebar 100 complies with the requirements set forth in AWSD1.1/1.1M-15 and the standards set forth in ACI 318-14.

As mentioned briefly above, ASTM A706/A706M provides a maximum CEV forsteel rebar material to be considered weldable. In particular, ASTMA706/A706M states that deformed bar material can have a CEV of up to0.55 percent and still be considered “weldable”. However, CEV values ashigh as 0.55 percent are not acceptable for stud-welding. Accordingly,the chemical composition of the steel material used to form rebar 100must be restricted to obtain an acceptable CEV range which ensures thestud-weldability of the rebar. The CEV of a chemical composition can becalculated according to the formula:

${CEV} = {{\%\mspace{14mu} C} + \frac{\%\mspace{14mu}{Mn}}{6} + \frac{\%\mspace{14mu}{Cu}}{40} + \frac{\%\mspace{14mu}{Ni}}{20} + \frac{\%\mspace{14mu}{Cr}}{10} - \frac{\%\mspace{14mu}{Mo}}{50} - {\frac{\%\mspace{14mu} V}{10}.}}$The following Table shows a preferred material composition for A706steel which achieves an acceptable range of CEV values. These valuesensure the stud-weldability of rebar 100. The material can be used tomake stud-weldable rebar 100 by restricting the CEV to a range of about0.31 percent to about 0.42 percent.

TABLE 2 Preferred A706 Material Composition for the Stud-Weldable RebarPreferred range, Element wt % Carbon (C)  0.08-0.230 Manganese (Mn)0.95-1.20 Phosphorous (P)  0.04 max Sulfur (S)  0.05 max Silicon (Si)0.2-0.4 Copper (Cu)  0.250 max Nickel (Ni)  0.150 max Chromium (Cr) 0.150 max Molybdenum (Mo) 0.001-0.050 Aluminum (Al) 0.001-0.020Vanadium (V) 0.030-0.080 Boron (B) 0.0005 max Nitrogen (N)  0.020 max

The restricted chemical composition listed in Table 2 above achieves aCEV in the range of about 0.31 percent to about 0.42 percent, which isacceptable for stud-welding. Applicant has surprisingly found that by:(a) hardening the rebar weld end as discussed in greater detail above;and (b) restricting the steel material composition to obtain a CEV inthe range of about 0.31-0.42% as shown in Table 2 above, a low-alloysteel deformed bar 100 can be provided which meets applicable industrystandards, including those set forth in ASTM A706/A706M, AWS D1.1/1.1M,and ACI 318-14.

An exemplary method for making the stud-weldable rebar 100 as shown inFIGS. 1-4 and as discussed above will now be described. The methodincludes providing a steel rebar body 102 with first and second ends104, 106 and a diameter D. Ignoring the height H of anyribs/deformations that may be present, and/or any other optional surfacefeatures of the rebar body 102 (e.g., chamfered edge portion 116described in further detail above), the rebar diameter D should besubstantially uniform at all points along length LA.

The chemical composition of the steel material which forms the rebarbody 102 should conform to the requirements of ASTM A706/A706M andshould also provide a CEV in the range of about 0.31-0.42%, such as thechemical composition detailed in Table 2 above. The method continues byrapidly heating and cooling a portion of the weld end 106 to formhardened zone 120. Stated another way, the method continues withincreasing the hardness at the tip portion 122 of weld end 106 by about1.5-3 times the hardness of the base portion 124 of rebar body 102,including about 2-2.5 times the hardness. Stated yet another way, thehardness at zone 120 of the tip portion 122 at weld end 106 is increasedby about 120-150%. The length L_(Z) of the hardened zone 120 is chosento be about 30-50% the diameter D of the rebar, including about 40% thediameter D of the rebar. The tip portion 122 at the weld end 106 caninclude a chamfered edge 116 formed between outer rebar surface 108 andterminal surface 114, and the chamfered edge extends a length L_(E) thatis about 20-45% the length L_(Z) of the hardened zone, including about22.5-40%. The tip portion 122 is also provided with a flux load 118fixed to the terminal surface 114 at the weld end 106, and the flux loadhas a length L_(F) that is about 10-25% the length of the hardened zoneL_(Z), including about 12.5-20%. Preferred hardened zone sizes,chamfered edge sizes, and flux load sizes for common rebar diameters andlengths are further detailed in Table 1 above.

The hardening process uses induction heating to rapidly heat a portionof the rebar tip 122 at the weld end 106. The rebar tip portion isheated until it reaches a target temperature which enablestransformation to martensite. In specific embodiments, induction heatingis applied for a period of about 4-9 seconds, until a target temperatureof about 1,300-1,700° F. is reached. After induction heating, the heatedweld end portion is allowed to rest for a dwell time of about 2 seconds.Immediately thereafter, the weld end portion is cooled by quenching in acooling medium for a period of about 5-12 seconds. As a result, amartensitic microstructure is formed at zone 120 which preferably has aconsistent Rockwell hardness from the outer surface to the core of therebar body 102 of about 20-50 HRC. Exemplary preferred sizes for theflux load 118 and chamfered edge 116 (if one is desired) are alsoprovided in Table 1 above. Once the preceding method is complete, rebar100 is provided with a weld end 106 which can be stud-welded to a basemetal in a manner that conforms with industry standards, such as thoseas set forth in at least AWS D1.1/1.1M and ACI 318-14. Preferredburn-off parameters for making such a weld are detailed in Table 1above.

In existing rebar products, the stud-welding process itself cansignificantly increase the hardness and strength at the tip or weldregion. However, the remaining portion of rebar does not see asignificant change in physical properties compared to the weld region.As a result, a disparity in physical properties can occur in existingrebar products, and this disparity can increase the likelihood offailure at the weld region. In contrast, by pre-hardening the weld endsas discussed herein, the pre- and post-weld physical properties can bebetter controlled. As a result, significant disparities inhardness/strength and the risk of failure at the weld connection areeliminated or reduced. Moreover, some guiding principles of weldedconnections are satisfied, including that the weld connection should beformed to have both: (a) a tensile strength which ensures the weld isnot the weakest link; and (b) a yield strength close to the that of theparent rebar so that accepted deformation requirements are met. Finally,by providing rebar with stud-weldability enabled at least in-partthrough the use of hardened weld ends as discussed herein, thecomparatively time-consuming pre-treatment or physical deformation stepsoften required in the prior art to assemble or install rebar areeliminated.

The exemplary embodiment has been described with reference to thepreferred embodiments. Obviously, modifications and alterations willoccur to others upon reading and understanding the preceding detaileddescription. It is intended that the exemplary embodiment be construedas including all such modifications and alterations insofar as they comewithin the scope of the appended claims or the equivalents thereof.

The invention claimed is:
 1. A stud-weldable rebar comprising: a steelbody having a weld end and a diameter that is substantially uniformalong a length of the steel body; and, a tip portion at the weld end anda base portion formed of the remaining steel body, the tip portionincluding a hardened zone, wherein the hardened zone has a hardnessabout 1.5-3.0 times greater than a hardness of the base portion.
 2. Thestud-weldable rebar of claim 1, wherein the hardness of the hardenedzone is about 2-2.5 times greater than the hardness of the base portion.3. The stud-weldable rebar of claim 1, wherein the hardness of thehardened zone is about 20-50 HRC.
 4. The stud-weldable rebar of claim 1,wherein the hardened zone has a length that is about 30-50% the diameterof the steel body.
 5. The stud-weldable rebar of claim 4, wherein thelength of the hardened zone is about 40% the diameter of the steel body.6. The stud-weldable rebar of claim 4, wherein the tip portion furthercomprises a terminal surface at the weld end and a chamfered edgeadjacent to the terminal surface, the chamfered edge extending a lengththat is about 20-45% of the length of the hardened zone.
 7. Thestud-weldable rebar of claim 6, wherein the chamfered edge lengthextends about 22.5-40% of the length of the hardened zone.
 8. Thestud-weldable rebar of claim 4, wherein the tip portion furthercomprises a terminal surface at the weld end and a flux load fixed tothe terminal surface, the flux load having a length that is about 10-25%of the length of the hardened zone.
 9. The stud-weldable rebar of claim8, wherein the length of the flux load is about 12.5-20% of the lengthof the hardened zone.
 10. The stud-weldable rebar of claim 1, whereinthe steel body has a chemical composition comprising 0.08-0.23 wt % ofcarbon, 0.95-1.2 wt % of manganese, less than 0.25 wt % of copper, lessthan 0.15 wt % of nickel, less than 0.15 wt % of chromium, 0.001-0.05 wt% of molybdenum, and 0.03-0.08 wt % vanadium.
 11. The stud-weldablerebar of claim 1, wherein the steel body has a chemical compositioncomprising 0.08-0.23 wt % of carbon, 0.95-1.2 wt % of manganese, lessthan 0.04 wt % of phosphorous, less than 0.05 M % of sulfur, 0.2-0.4 wt% of silicon, less than 0.25 wt % of copper, less than 0.15 wt % ofnickel, less than 0.15 wt % of chromium, 0.001-0.05 wt % of molybdenum,0.001-0.02 wt % of aluminum, 0.03-0.08 wt % vanadium, less than 0.0005wt % of boron, and less than 0.02 wt % of nitrogen.
 12. Thestud-weldable rebar of claim 1, wherein the steel body has a chemicalcomposition comprising a carbon equivalency value between 0.31-0.42%.13. A stud-weldable rebar comprising: a steel body having a first end, aweld end, and a generally cylindrical outer surface, the outer surfacedefining a diameter that is substantially uniform along all points ofthe steel body; a tip portion at the weld end, the tip portion includinga hardened zone, a terminal surface, and a flux load fixed to theterminal surface; and, a base portion defined between the first end andthe tip portion of the steel body, wherein the hardened zone has alength that is about 30-50% of the diameter of the steel body and ahardness that is about 1.5-3.0 times greater than a hardness of the baseportion of the steel body.
 14. The stud weldable rebar of claim 13,wherein the hardness of the hardened zone is about 20-50 HRC and thehardness of the base portion is about 90-98 HRB.
 15. The stud-weldablerebar of claim 13, wherein the length of the hardened zone is about0.150-0.400 inch.
 16. A stud-weldable rebar comprising: a steel bodyhaving a weld end; and, a tip portion at the weld end and a base portionformed of the remaining steel body, the tip portion including a hardenedzone, wherein the hardened zone has a hardness about 1.5-3.0 timesgreater than a hardness of the base portion; and wherein the steel bodyhas a chemical composition comprising 0.08-0.23 wt % of carbon, 0.95-1.2wt % of manganese, less than 0.25 wt % of copper, less than 0.15 wt % ofnickel, less than 0.15 wt % of chromium, 0.001-0.05 wt % of molybdenum,and 0.03-0.08 wt % vanadium; and wherein the chemical compositioncomprising a carbon equivalency value of about 0.31% to about 0.42%. 17.The stud-weldable rebar of claim 16, wherein the steel body has adiameter that is substantially uniform along a length of the steel body;and wherein the diameter is ⅜″, ½″, ⅝″, ¾″, ⅞″, or 1″.
 18. Thestud-weldable rebar of claim 17, wherein the hardened zone has a lengththat is about 30-50% the diameter of the steel body.
 19. Thestud-weldable rebar of claim 18, wherein the tip portion furthercomprises a terminal surface at the weld end and a chamfered edgeadjacent to the terminal surface, the chamfered edge extending a lengththat is about 20-45% of the length of the hardened zone.
 20. Thestud-weldable rebar of claim 18, wherein the tip portion furthercomprises a terminal surface at the weld end and a flux load fixed tothe terminal surface, the flux load having a length that is about 10-25%of the length of the hardened zone.